1. Field of the Invention
The present invention relates to a sample injector used to inject a sample during chromatography in which a liquid or a gas is used as the sample.
2. Description of the Related Art
A sample injector used in liquid chromatography may be typically constituted using a flow passage switch valve. The flow passage switch valve realizes injection of a sample solution into a mobile phase solvent by switching appropriately between a mobile phase solvent flow passage and a sample solution flow passage. More specifically, FIG. 1 shows a conventional example employing a well-known hexagonal switch valve 99. The hexagonal switch valve 99 includes six ports numbered from 1 to 6, and realizes two flow passage states for sample charging (also referred to as loading) and sample injection, respectively.
During sample charging, two ports having port numbers 2 and 3 are connected such that the mobile phase solvent flow passage is formed from a pump to a column for separating the sample. At this time, two ports having port numbers 1 and 6 are connected simultaneously, and therefore a sample solution flow passage is formed from a port having a port number 4 to the port (a drain) having the port number 6 via a sample loop 98. As a result, the sample solution is loaded into the sample loop 98 from the port having the port number 4 using a syringe (not shown) while surplus liquid is discharged from the sample loop 98. During injection, on the other hand, the two ports having the port numbers 1 and 2 are connected and the two ports having the port numbers 3 and 4 are connected. Thus, a flow passage through which the sample loaded into the sample loop 98 is caused to flow back by a discharge pressure from the pump and thereby injected into the column is formed.
In the related art, this flow passage switching operation is typically performed by bringing two flat surfaces including a plurality of through holes into contact with each other and switching communication states between the plurality of through holes in the respective flat surfaces by rotationally sliding the flat surfaces against each other (Japanese Patent Application Publication No. H4-25683, Japanese Patent Application Publication No. H8-5621, Japanese Patent Application Publication No. 2003-185645, and Japanese Patent Application Publication No. 2007-121164). Meanwhile, a sample solution amount is measured on the basis of the syringe for injecting the sample or the amount of discharged surplus liquid.
When the communication states among the plurality of through holes in the related art are switched by a sliding motion, however, a complicated high-precision and an elastic sealing member must be used to realize the sliding motion, and a device for measuring the amount of injected sample as described above is also required. Such a complicated mechanism has a large number of components and is therefore difficult to reassemble after cleaning. Moreover, the present inventor has discovered that adjustments required during reassembly are difficult, making it difficult to maintain an initial performance. The present inventor also discovered that when an elastic sealing member is used, problems are likely to arise in terms of increases in the number of components, infiltration of foreign matter, and reduced wear life.